Particle beam microscopy is a powerful tool for investigating the topography and the chemical composition of object surfaces. Examples of such particle beam microscopes are scanning electron microscopes and helium ion microscopes. They combine high resolution with a wide magnification range. The wide magnification range allows features of an object of different length scales to be investigated. In particular, regions of interest on the object surface may be identified at a low magnification level and later be imaged at a high magnification.
However, in commonly available scanning electron microscopes, it is difficult to reliably determine the exact three-dimensional shape of the object surface solely on the basis of micrographs and without varying the tilt angle of the electron beam with respect to the object surface. As a general rule, the signal height of a secondary electron detector depends on a tilt angle of the surface portion, which is irradiated with the primary electron beam. However, images which have been acquired with a secondary electron detector, also show some atomic number contrast and are influenced by a variety of other effects, such as edge enhancement.
Therefore, typically the three-dimensional topology of the object surface has to be guessed from the image data of the micrograph as it appears on the screen or a printout, often allowing for multiple interpretations.
On the other hand, three-dimensional integrated circuits in which two or more layers of active electronic components are integrated both horizontally and vertically into a single circuit are widely considered to be a promising technology for the future. In order to develop manufacturing technologies for this kind of semiconductor devices, it is advantageous to have reliable and efficient procedures to study the surface topography of objects.
Accordingly, it is considered desirable to provide a method and an apparatus for efficiently inspecting the topography of an object surface by using a scanning particle beam microscope.